Many scientific or applied investigations of brain function depend on an assessment of the degree of activation of a particular brain area. More formally, this degree of activation can be expressed by measurements of cortical excitation or cortical excitability. Cortical excitation describes the degree of activation of a particular area of the brain. Cortical excitability describes the likelihood that a particular area of the brain gets excited. Thus, the two measurements are closely related: on average, the higher cortical excitability in a certain area of the brain, the higher its excitation.
Accurate measurements of cortical excitability are very important. First, certain brain signal measurement modalities cannot directly measure cortical excitation. For example, scalp-recorded EEG cannot readily access brain activity at those high frequencies (typically >40 Hz) that index cortical excitation. Second, in certain application domains, it may be important to measure cortical excitability instead of cortical excitation. For example, the human faculty of attention (e.g., when one expects to hear a tone compared to seeing something) is realized by the brain by regulating the degree of cortical excitability, e.g., increasing cortical excitability in auditory brain areas, and decreasing excitability in visual brain areas.
It has long been known that a principal mechanism of the brain to regulate cortical excitability is to change specific properties of oscillations across different areas of the brain. In particular, many previous studies have linked the power or the phase of cortical oscillations to cortical excitability. However, there still exists the need for more accurate ways of measuring and predicting cortical excitation.
The present invention is directed to overcoming these and other deficiencies in the art.